re: I like how the Dutch preposition on and the definite article der got reanlysed as the English preposition under (which is cognate with the English (via Latin) words inferior, infernal, &c.,

wouldn't the on/un perception depend a lot on how the dutch said on/(and how the english did?)

a maternal aunt was MAR ee (mar like to mar the surface)

we kids heard MARY, but my mother was saying Marie. they gave up trying to correct us, (or perhaps never heard what we were saying) and she became aunt Mary.

it wasn't till i was an adult that i heard MARee as Marie.
(by then i had traveled to both Ireland and UK and had a better ear.)

(i don't know any dutch (and haven't heard much spoken dutch) to know, and besides, i presume spoken dutch has change as much as spoken english over the centuries. could it be that onderway sounded like underway?